Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor to compress air that is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture. The compressor and the turbine include disks. The disks include slots that seat blades. A slot in a disk holds a blade in place and resists centrifugal forces that would otherwise cause the blade to become detached from the disk.
Referring to FIG. 2A, a system 200 for forming a slot 206 in a disk 212 is shown. In particular, a broach tool 218 is used to machine the slot 206 in the disk 212. The broach tool 218 is initially applied to the disk 212 at an entrance/surface 212a of the disk 212. Continued application of the broach tool 218 (e.g., teeth 218a of the broach tool 218) to the disk 212 causes material of the disk 212 to be removed; this removal of material forms the slot 206 in the disk 212.
Referring to FIG. 2B, the slot 206 is shown in greater detail. As shown, the slot 206 frequently is of a “fir-tree” profile in terms of a shape/pattern of, e.g., walls 212b and 212c of the disk 212 that remain following the removal of the material as described above. More generally, the shape of the slot 206 may match a shape of a root of a blade.
Referring to FIGS. 2A-2C, often the slot 206 is not parallel to a normal ‘N’ of the disk 212 at, e.g., the surface 212a. Instead, an axis ‘A’ of the slot 206 is oriented at an angle ‘θ’ (referred to herein as a slash angle) with respect to the normal ‘N’. The value of the slash angle is usually between three and fifteen degrees.
Due to the slash angle, the broach teeth 218a are not subjected to equal forces/loads on either side of the broach tool 218, which is to say that the broach teeth 218a experience asymmetrical forces/loads. Due to finite stiffness of the broach teeth 218a, the teeth 218a deflect in the presence of force/load. The deflection potentially causes dimensional errors or quality problems in the slot 206. Such dimensional errors/quality problems may be manifested as waviness in the slot 206/walls 212b-212c. Still further, the deflection may result in a deviation in terms of material removal relative to a specification of the slot 206/walls 212b-212c. 
An expendable chip ring 230 is often used in conjunction with an exit 212d of the disk 212 (where the term/label ‘exit’ is referenced relative to the completion of the broaching process with respect to the disk 212). The chip ring 230 is used so that any burr that is produced is left on the chip ring 230 rather than on the disk 212. The chip ring 230 helps to maintain a temperature profile at the exit 212d of the disk 212 within specified limits, ensuring that any burr that is formed is present on the chip ring 230 (and not on the disk 212). The chip ring 230 provides thermal mass ahead/in advance of the broach tool 218 so that chips shear with an adequately high shear angle (e.g., with a shear angle greater than a threshold); this ensures that degradation to the disk 212 due to cessation of chip formation when the broach tool 218 exits the disk 212 and enters the chip ring 230 is small (e.g., less than a threshold). Frequently, the chip ring 230 is held tightly against the exit side of the disk 212 between the disk and a backing fixture during the formation of the slot 206 to limit/reduce/minimize the extent that the disk 212 deflects. A chip ring (e.g., chip ring 230) may also be referred to as a thermal ring or force ring herein.
Three material properties impact the errors/quality problems described above: (1) material elasticity, (2) hardness, and (3) machinability. Material elasticity relates to the disk 212/chip ring 230 stiffness, and is a representation of a degree to which the disk 212/chip ring 230 deflect in the presence of a force resulting from the application of the broach tool 218. Hardness relates to the machining forces that would be exhibited when the broach tool 218 is penetrating the material of the disk 212/chip ring 230. Machinability relates to the level of wear sustained by the broach tool 218 for a given tool traversal length. An improved approach for forming a slot that takes into account the foregoing, including the aforementioned material properties, is needed.